As a sound field control technique which increases sound pressure in a specific area, and maintains sound pressure in another area, for example, a sound spot or sound collector using a time delay is known. This technique targets at mid/treble tones, and increases bass tones in both an area for increasing mid/treble tones and an area for maintaining mid/treble tones. A superdirectional parametric speaker using ultrasounds is also unsuitable for bass tones.
On the other hand, a sound field control technique which can target at bass tones is also known. This technique maintains sound pressure in an area in front of a speaker, and reduces sound pressure in a surrounding area. Upon reducing sound pressure, uniform frequency characteristics cannot be provided.
No conventional control technique which increases bass tones in a specific area, can maintain sound pressure in another area, and can give uniform frequency characteristics in association with sound pressure maintenance is known.